I'm surprised there isn't a thread about this in GD as it isn't really about the games or the consumer, its all about Epic wanting to get more profit for themselves and more control. I find it highly interesting that they are not going after the console market given the cut is exactly the same. Let's not forget that Sony has a significant stake in Epic and was an Apple 'competitor' in the mobile phone space. Now Tencent also has a significant stake and all of the current shenanigans with them and trump, who knows who is pulling the strings here?
Back in the day of retail distribution these companies would have paid up to 70% to the retailer, 30% isn't completely extortionate given what Apple and Google actually provide.
They have both built up the platform from scratch, built the user base, built the store, built all the development tools and offer them to developers for next to nothing, they offer space on the app store for free, they promote good content for free, they only actually charge the developer when they sell something. Developers don't pay for all of the bandwidth needed to distribute the content, not do they pay them to review apps to ensure the quality is good enough.
That said I can see why Epic want a bigger piece of the pie, it's all business at the end of the day.